Optical properties of new aliphatic–aromatic co-polyimides

Optical transmission of a series of aliphatic–aromatic co-polyimides have been investigated in the range 200–3000 nm. The short wavelength edge of transmission depends on the ratios of diamines (aliphatic to aromatic) and on the type of aliphatic diamine. To obtain the optical parameters the approach proposed by Tauc for amorphous semiconductors has been used, because of the similarity of the absorption edges. The values of pseudogaps were found from 1.01 to above 4 eV, while the Urbach energy changed in the range 75–800 meV. All determined parameters have been found to be related to the influence of the polymer chain structure.